1. Technical Field
The present invention relates to a spacing device (stent) for use in fenestrations of the paranasal sinus.
2. Related Art
About 5% of our population suffer from a chronic mucous membrane inflammation of the paranasal sinuses. In the course of an inflammation of this type, nasal polyps occur in every fifth patient. If corresponding symptoms occur and an attempt at medicinal treatment remains unsuccessful, the chronic sinusitis is approached surgically.
The paranasal sinus system consists of a series of cavities lined with mucous membrane and filled with air. The interruption of the natural secretion drainage from the remote paranasal sinus portions and the removal of natural ventilation are important in the occurrence of chronic sinusitis. The remote, diseased paranasal sinus portions are accordingly reventilated during cleaning-up interventions through newly created or extended accesses (“windows”). After healing, the natural secretion drainage of these reventilated compartments reappears.
Surgical treatment of chronic sinusitis has been transformed after the introduction of modern optical aids (rigid endoscopes, microscope). Nowadays, the “minimally invasive” clearing exclusively of those mucous membrane parts which have undergone an obviously irreversible change owing to the inflammation process predominates. Other reversibly changed or unaffected mucous membrane areas are spared as far as possible (Hosemann W G, Weber R K, Keerl R E, Lund V J: Minimally invasive endonasal sinus surgery. Thieme, Stuttgart, New York 2000).
If the frontal sinus mucous membrane is involved in the inflammatory modification of the sinus a surgical fenestration takes place towards the nose. This is carried out with special instruments (bent sharp spoons, special stamps, drills). Accesses of about 5 to a maximum of 10 mm in diameter are produced by routine “fenestration” of the frontal sinus. During healing of the wound these accesses narrow by about 1.5 mm.
If certain health factors are present, such as, for example intolerance of analgesics, a disproportionate tendency to scarred narrowing has to be taken into account (Hosemann W, Th. Kühnel, P. Held, W. Wagner, A. Felderhoff: Endonasal frontal sinusotomy in surgical management of chronic sinusitis—a critical evaluation. Am. J. Rhinology 11: 1-9 (1997)). In such cases it is advised to maximise the surgical access as a precaution. This “widened frontal sinus surgery” is subdivided into specific types (Draf W: Endonasal micro-endoscopic frontal sinus surgery: the Fulda concept. Op Tech Otolaryngol Head Neck Surg 2: 234-240 (1991); May M, Schaitkin B: Frontal sinus surgery: endonasal drainage instead of an external osteopolstic approach. Op Tech Otolaryngo Head Neck Surg 6: 184-192 (1995)).
As stated, the neo-ostium to the front sinus narrows to a greater or lesser extent, according to experience. To prevent this scarred stenosis it was already proposed at the start of the last century, i.e. long before the introduction of minimally invasive endoscopic surgery to insert a spacing device (stent). These spacing devices usually had the form of a small tube and were made of various materials: at the beginning rolled metal or metal braided in wires was used (Fletscher Ingals E: New operation and instruments for draining the frontal sinus. Ann Otol Rhinol Laryngol 14: 515-519 (1905), Good R H: An intranasal method for opening the frontal sinus establishing the largest possible drainage. Laryngoscope 18: 266-274 (1908)). In the last two decades silicone tubes were preferred (Stammberger H: Komplikationen entzündlicher Nasennebenhöhlenerkrankungen eischlieβlich iatrogen bedingter Komplikationen. Eur Arch Oto-Rhino-Laryngol Suppl 1993/1: 61-186).
Experience with spacing devices for stabilising the newly created frontal sinus access was not always, however, encouraging, apart from individual reports (Jacobs J B: 100 years of frontal sinus surgery. Laryngoscope 107: 1-36 (1997); Weber, R, W. Hosemann, W. Draf, R. Keerl, B. Schick, S. Schinzel: Denonasale Stirnhöhlenchirugie mit Langzeiteinlage eines Platzhalters. Laryngol. Rhinol. Otol. 76: 728-734 (1997).
Initially it remained unclear as to how long a spacing device of this type was required in the area of the operation. From animal experiments on wound healing, it became clear that a scarred narrowing of the frontal sinus access for a post-operative period of at least three months has to be assumed (Hosemann, M. E. Wigand, U. Göde, F. Länger, I. Dunker: Normal wound healing of the paranasal sinuses—clinical and experimental investigations, Eur. Arch, Otorhinolarylgol. 248: 390-394 (1991)). Accordingly, the spacing device would have to be used over eight to twelve weeks. Even with the correct duration in position a spacing device will often only delay and possibly reduce in scope the undesired scarred narrowing, without being able to prevent it completely. An additional medicinal treatment to reduce excessive wound reactions would have to take place here.
According to the present level of knowledge about wound healing processes in the nose the administration of medicinal substances such as, for example, corticosteroids, seems to be in a position to counteract, with a certain reliability, this tendency to regenerating mucous membrane for scarred stricture of the front sinus nose passage (Hosemann, M. E. Wigand, U. Göde, F. Länger, I. Dunker: Normal wound healing of the paranasal sinuses—clinical and experimental investigations. Eur. Arch. Otorhinolaryngol. 248: 390-394 (1991); Hosemann W, Göde U, Länger F, Wigan M E: Experimentelle Untersuchungen zur Wundheilung in den Nasennebenhöhlen. II. Spontaner Wundschluss und medikamentöse Effekte im standardisierten Wundmodell. HNO 39{umlaut over ( )}48-54 (1991); Hosemann W, Kühnel Th, Allert M H: Weiterbehandlung nach Nasennebenhöhleneingriffen, part 2: Theapeutische Maβnahmen, HNO aktuell 7: 291-302 (1999).
Unfortunately, conventional medicine forms such as salves or sprays do not reach into the problem region of the transition of frontal sinus and nose during routine application (Prince M E P, Lemckert R J: Analysis of the intranasal distribution of ointment. J Otolaryngol 26: 357-360 (1997); Weber R, Keerl R, Radziwill R, Schick B, Haspersen D, Dshambazov K, Mlynski G, Draf W: Videoendoscopic analysis of nasal steroid distribution. Rhinology 37: 69-73 (1999)).
Postoperative systemic administration of corticosteroids is certainly usual in rhinosurgery (Bumm P: Hals-Nasen-Ohrenkrankheiten. In: Kaiser H, Kley H K (Hrsg.) Cortizontherapie, Corticoide in Klinik und Praxis. Thieme, Stuttgart 1992, pages 390-401), but the treatment plans do not usually extend over the required duration of 8 weeks. Moreover, with longer-term systemic corticosteroid administration side effects of the treatment have to be increasingly taken into account.
The presently described problems show the need for systems which can in a controlled manner dispense the active substances such as, for example, corticosteroids over a longer period directly to the operation site.
A series of systems have been proposed for the controlled release of medicinal substances such as, for example implants of polymers loaded with a medicinal substance. U.S. Pat. No. 5,633,000 thus describes implants for the release of pain killers. The polymers used there release the active substance via diffusion. U.S. Pat. No. 5,019,372 describes that this release can be modulated by incorporation of magnetic particles and by application of alternating magnetic fields. If this formed body is designed with a correspondingly defined geometry the release of the active substances can be optimised such that they are released over the application period at a constant speed (U.S. Pat. No. 4,803,076).
The polymers used for such applications include, apart from biodegradable materials, non-biodegradable materials, i.e. those which do not decompose on contact with body fluids. Examples of such polymers are silicone, polyacrylate and ethylene vinyl acetate copolymer (U.S. Pat. No. 4,069,307). The last polymer group, in particular, was used for a series of systems for controlled release of active substances.
U.S. Pat. No. 3,393,073 thus describes a so-called reservoir system consisting of a medicinal substance reservoir which is surrounded by a polymer sheath regulating the release rate of the medicinal substance. Such systems were successfully used for the development of “intra-uterine devices” which release the active substance in the uterus (U.S. Pat. No. 3,967,618 and U.S. Pat. No. 4,016,251) and for producing therapeutic systems which release medicinal substances to the eye (U.S. Pat. No. 4,052,505).
Such systems were also described, as carrier systems with a microporous membrane controlling the discharge of the active substance, for introduction into various body cavities, such as for example, the ear, nose or the rectum (U.S. Pat. No. 3,948,254).
Those made of plastics are described in the area of “stents” for the treatment of paranasal sinuses, such as, for example in U.S. Pat. No. 5,693,065 or U.S. Pat. No. 5,336,163. U.S. Pat. No. 5,693,065 describes a stent for the nose area made of silicone rubber having a cylindrical shaft of which the leading end to be inserted into the nose is designed in the shape of the point of a spear, the base of the point connected to the shaft having a wider diameter than the shaft. The point is closed at the front and laterally has ribs with slits therebetween, the ribs expanding in the inserted state and thus ensuring the hold of the stent in the nose area.
An external diameter of 0.157 inches and an internal diameter of 0.118 inches is given as the dimensions for the shaft. The firm seat of the stent in the nose passage is only ensured, however, by the spreading of the spear-shaped point.
U.S. Pat. No. 5,336,163 relates to a stent for the nose area formed from a porous material and having a non-adhering, but slightly porous outer surface. The stent is formed from a material here which expands on contact with liquid.
U.S. Pat. No. 5,601,594 describes a stent for insertion into a nose aperture, the stent having a bent shape and being formed from a compressible material.
However, these are systems which are free of medicinal substances and the action of which only aims to keep open the accesses to the frontal sinus by physical/mechanical effects.
Despite this progress in the area of controlled release of active substances there has previously not been any indications that this technology could be usable for the post-operative care of sinus systems after minimally invasive clearing. Although so-called “stents” which prevent a tissue reconstruction are known these are described exclusively for the treatment of blood vessels and are accordingly geared to other biological needs.
U.S. Pat. No. 5,980,551 describes a stent for blood vessels, the stent having an inner support structure which may be formed from a wire and the support structure is surrounded by a biodegradable resorbable substrate. Biologically active microparticles which release active substances in a controlled manner can be embedded into this substrate.
Stents for suppressing the restenosis of coronary arteries have design features which clearly differ from the subject of the invention and therefore also make them unsuitable for application in the frontal sinus.
In many cases the “coronary stents” also require application aids. Such application aids are described in combination with a stent in U.S. Pat. No. 6,080,190 and U.S. Pat. No. 5,843,089. A serious problem of coronary stents to release active substances is the construction of the medicinal substance release system. Coronary stents generally consist of a stent body such as, for example, a wire braiding covered with medicinal substance-carrying polymers or sheathed in thin polymer films (U.S. Pat. No. 5,824,048, U.S. Pat. No. 5,700,286, U.S. Pat. No. 5,837,313, U.S. Pat. No. 5,679,400). The mechanical stability of these stents is geared to the needs of arteries and makes them unsuitable for application in the nasal sinus, as they are not mechanically stable enough.
Coronary stents are rotationally symmetrical hollow bodies and preferably have the geometry of a hollow cylinder. They can therefore not be fixed via thickenings at the cylinder end in a fenestration of the paranasal sinus. Moreover, a fenestration of the paranasal sinus is generally not uniformly round, but more or less irregular which creates additional problems with respect to anchoring. In general, coronary stents cannot have large wall thicknesses so as not to impede the blood flow.
Moreover, coronary stents differ from spacing devices for paranasal sinuses due to their function. The coronary stent is intended to expand the vessel in many cases. The front sinus spacing device, on the other hand, is inserted in a surgically applied passage which has bony (stable) walls. This passage was surgically newly formed; the coronary artery, on the other hand is left as a tube, but expanded.
A coronary stent is a permanent implant, it is completely absorbed by the body. The frontal sinus spacing device, on the other hand, is removed after a period of about 8 weeks.
The coronary stent is completely absorbed by the body. Blood flows in the interior of the coronary stent; the wall is completely colonised in the most favourable case by the body's own cells (endothelial cells). With the frontal sinus spacing device, complete absorption into the body is not desirable. Secretion from the mucous membrane surface should drain in the interior of the frontal sinus spacing device and ventilation should simultaneously be ensured. Colonisation of the interior of the spacing device with the body's own cells is neither anticipated nor desired.
On the other hand, the mucous membrane should widen at the outside of the frontal sinus spacing device. In this manner, once the spacing device has been removed, a passage lined with intact mucous membrane should remain.
A problem in the coronary stent is the formation of a clot with the risk of an occlusion which has to be suppressed by the administration of special medication. The frontal sinus spacing device does not require the administration of special medication.
It has been proposed to produce medical devices used in the body from a material loaded with active substance or to coat them therewith.
WO 96/29071 describes medical devices such as catheters or stents, on the surface of which antibacterial means are applied, the antibacterial means adhering to the surface owing to adhesive forces, without further aids being required.
It is proposed in general in WO 92/15286 to form medical devices from a polymer loaded with medicinal substance or to provide them with a coating thereof, stents also being mentioned for use in the nasal area, without more detail about the configuration of a stent of this type.